Josephson ac/dc converter systems and method

ABSTRACT

One embodiment describes an AC/DC converter system. The system includes a flux-shuttle loop that is inductively coupled with an AC input signal. The system also includes a plurality of Josephson junctions spaced about the flux shuttle loop that are configured to sequentially trigger in response to the AC input signal and to provide a single-flux quantum (SFQ) pulse that moves sequentially around the flux-shuttle loop that results in a DC output signal being provided through an output inductor.

TECHNICAL FIELD

The present invention relates generally to quantum and classical digitalsuperconducting circuits, and specifically to a Josephson AC/DCconverter systems and method.

BACKGROUND

Superconducting digital technology has provided computing and/orcommunications resources that benefit from unprecedented high speed, lowpower dissipation, and low operating temperature. Superconductingdigital technology has been developed as an alternative to CMOStechnology, and typically comprises superconductor based single fluxsuperconducting circuitry, utilizing superconducting Josephsonjunctions, and can exhibit typical signal power of around 4 nW(nanowatts) at a typical data rate of 20 Gb/s (gigabytes/second) orgreater, and can operate at temperatures of around 4° Kelvin. TheJosephson junction is an active device that is supplied with a DC biascurrent, and the power budget in such circuits is dominated by staticpower consumption which happens whether or not the active device isswitching. Typical systems can provide the DC bias current directlyusing a bias resistor network, which can result in substantially highcurrents (equal to or greater than an amp), which can result in spuriousmagnetic fields and heat resulting from high power dissipation.

SUMMARY

One embodiment describes an AC/DC converter system. The system includesa flux-shuttle loop that is inductively coupled with an AC input signal.The system also includes a plurality of Josephson junctions spaced aboutthe flux shuttle loop that are configured to sequentially trigger inresponse to the AC input signal and to provide a single-flux quantum(SFQ) pulse that moves sequentially around the flux-shuttle loop thatresults in a DC output signal being provided through an output inductor.

Another embodiment includes a method for providing a DC output signalbased on an AC input signal. The method includes providing aninitialization bias current to a flux-shuttle loop comprising aplurality of stages. The method also includes providing the AC inputsignal that is inductively coupled with each of the plurality of stages.The method further includes sequentially triggering a Josephson junctionassociated with each of the plurality of stages based on a frequency ofthe AC input signal to circulate a single-flux quantum around theflux-shuttle loop to generate the DC output signal through an outputinductor.

Another embodiment includes an AC/DC converter system. The systemincludes a flux-shuttle loop comprising a plurality of stages and beingconfigured to receive an AC input signal. Each of the plurality ofstages includes a transformer configured to generate a bias currentbased on inductive coupling of the AC input signal to the respective oneof the plurality of stages. Each of the plurality of stages alsoincludes a Josephson junction configured to trigger to provide asingle-flux quantum in response to the bias current. Each of theplurality of stages also includes an inductor interconnecting therespective one of the plurality of stages with the output inductor andbeing configured to provide a current pulse in response to thesingle-flux quantum. The system also includes an output inductor coupledto each of the storage inductors and being configured to provide the DCoutput signal based on the received current pulse outputs that aresequentially provided from each of the storage inductors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a superconducting circuit system.

FIG. 2 illustrates an example of a Josephson AC/DC converter.

FIG. 3 illustrates an example of a timing diagram.

FIG. 4 illustrates an example of a superconducting circuit system.

FIG. 5 illustrates an example of a method for providing a DC outputsignal based on an AC input signal.

DETAILED DESCRIPTION

The present invention relates generally to quantum and classical digitalsuperconducting circuits, and specifically to a Josephson AC/DCconverter systems and method. The Josephson AC/DC converter includes aflux-shuttle loop comprising a plurality of stages. Each of theplurality of stages comprises a transformer, at least one Josephsonjunction, and an inductor. The transformer is configured to inductivelycouple an AC input signal to the flux-shuttle loop, such that the ACinput signal provides a bias current in the flux-shuttle loop. Theflux-shuttle loop also includes an initialization transformer configuredto generate a bias current in response to a DC initialization signal.Thus, in response to the bias current provided via the initializationtransformer and the bias current provided by the AC input signal via thetransformers in each of the stages, the Josephson junction(s) in each ofthe stages triggers to provide a single-flux quantum (SFQ) pulse aroundthe flux-shuttle loop based on the frequency of the AC input signal. Asan example, the SFQ pulse can propagate through a given stage at eachpositive and negative cycle of the AC input signal. The SFQ pulse isprovided to the inductor of each of the plurality of stages to provide acurrent pulse to an output inductor, such that the output inductorprovides a DC output signal.

As an example, the AC input signal can include an in-phase AC inputsignal and a quadrature-phase AC input signal, and the flux-shuttle loopcan include four stages. A primary winding of the transformers of two ofthe stages can have an opposite polarity relative to a primary windingof the transformers of the other two of the stages. Therefore, on apositive cycle of each of the in-phase AC input signal and thequadrature-phase AC input signal, the bias current induced in secondarywindings of the transformers in two of the stages can be provided in agiven direction around the flux-shuttle loop, and on a negative cycle ofeach of the in-phase AC input signal and the quadrature-phase AC inputsignal, the bias current induced in secondary windings of thetransformers in the other two of the stages can be provided in the samegiven direction around the flux-shuttle loop. Therefore, the Josephsonjunction(s) in each of the stages can sequentially trigger at each 90°of the AC input signal to rotate the SFQ pulse around the flux-shuttleloop to provide current pulses to the output inductor to generate the DCoutput voltage.

FIG. 1 illustrates an example of a superconducting circuit system 10. Asan example, the superconducting circuit system 10 can be implemented inany of a variety of quantum computing applications, such as quantummemory or processing systems. The superconducting circuit system 10includes a device 12 that receives a DC signal, demonstrated in theexample of FIG. 1 as a DC current I_(DC). As an example, the DC signalI_(DC) can be provided as a power signal or as a driver signal to drivethe device 12. For example, the device 12 can correspond to a memorydriver, such as to provide a read current or a write current to a memorycell.

The superconducting circuit system 10 also includes a Josephson AC/DCconverter 14 that is configured to convert an AC input signal AC to theDC signal I_(DC). As an example, the AC input signal AC can be asinusoidal waveform having a substantially constant frequency (e.g.,approximately 10 GHz) and a low AC current magnitude, such as applicableto reciprocal quantum logic (RQL) superconducting circuits (e.g.,approximately 2 mA RMS). The Josephson AC/DC converter 14 isdemonstrated as receiving an initialization signal INTL that can beprovided to the Josephson AC/DC converter 14 to initialize the operationof the Josephson AC/DC converter 14 to convert the AC input signal AC tothe DC signal I_(DC). As an example, the initialization signal INTL canbe a DC signal that is substantially continuously provided to theJosephson AC/DC converter 14 to maintain the AC/DC conversion operationof the Josephson AC/DC converter 14. For example, the initializationsignal INTL can induce a bias current.

In the example of FIG. 1, the Josephson AC/DC converter 14 includes aflux-shuttle loop 16. The flux-shuttle loop 16 can include a pluralityof stages that are configured to transfer a single-flux quantum (SFQ)pulse around the flux-shuttle loop 16 during the AC/DC conversionoperation of the Josephson AC/DC converter 14 based on the frequency ofthe AC input signal AC. As described herein, the term “loop” withrespect to the flux-shuttle loop 16 describes a substantially continuousloop (e.g., circular) arrangement of the stages of the flux-shuttle loop16, such that a first stage can be coupled to a last stage. Therefore,the SFQ pulse can substantially continuously propagate around theflux-shuttle loop 16 while the initialization signal INTL is provided.

The flux-shuttle loop 16 can be arranged without resistors. As anexample, each of the stages of the flux-shuttle loop 16 can include atransformer, at least one Josephson junction, and an inductor. Thetransformer can be configured to inductively couple the AC input signalAC to the flux-shuttle loop 16, such that the AC input signal ACprovides a bias current in the flux-shuttle loop 16. The bias currentinduced by the AC input signal AC via the transformer can be added tothe bias current generated via the initialization signal INTL. Thus, inresponse to the collective bias currents, the Josephson junction(s) ineach of the stages of the flux-shuttle loop 16 triggers to generate theSFQ pulse that propagates around the flux-shuttle loop 16 based on thefrequency of the AC input signal AC. As an example, the SFQ pulse canpropagate through a given one of the stages at each positive andnegative cycle of the AC input signal AC. The SFQ pulse, as itpropagates around the flux-shuttle loop 16, can be provided to theinductor of each of the stages of the flux-shuttle loop 16 to provide acurrent pulse, such as to an output inductor in the Josephson AC/DCconverter 14 (not shown). Therefore, the DC signal I_(DC) can flowthrough the output inductor based on the current pulses beingsequentially provided to the output inductor based on the frequency ofthe AC input signal AC. For example, the current pulses can be generatedbased on the SFQ pulses providing a small voltage (e.g., approximately 2μV/GHz) to each of the inductors, such that the resulting current pulsescan be integrated in the output inductor to provide the DC signalI_(DC).

The Josephson AC/DC converter 14 can therefore operate to convert the ACinput signal AC to the DC signal I_(DC) in a power efficient manner. Asdescribed previously, the Josephson AC/DC converter 14 can beimplemented without resistors. Therefore, the Josephson AC/DC converter14 only dissipates power via the current pulses to provide the DC signalI_(DC) to the device 12, such that no additional power is dissipated tomaintain the SFQ pulse propagating around the flux-shuttle loop 16. Inaddition, the Josephson AC/DC converter 14 can generate substantially noheat from static power dissipation, as opposed to typicalresistance-based DC power sources. Accordingly, the Josephson AC/DCconverter 14 can operate more efficiently and effectively than typicalAC/DC converters, particularly in a quantum computing environment. Forexample, upon the DC output signal I_(DC) achieving an approximatelymaximum amplitude, the initialization signal INTL can be deactivated. Asa result, the Josephson junction(s) in each of the stages of theflux-shuttle loop 16 no longer sequentially trigger, but the DC outputcurrent IDC maintains the amplitude without dissipation so long as theload is quiescent (e.g., superconducting).

FIG. 2 illustrates an example of a Josephson AC/DC converter 50. TheJosephson AC/DC converter 50 can correspond to Josephson AC/DC converter14 in the superconducting circuit system 10. Therefore, the JosephsonAC/DC converter 50 includes a flux-shuttle loop 52 that includes aplurality of stages, demonstrated in the example of FIG. 2 as a firststage 54, a second stage 56, a third stage 58, and a fourth stage 60.The stages 54, 56, 58, and 60 are sequentially coupled to form a looparrangement. The Josephson AC/DC converter 50 is configured to convertan AC input signal to a DC output signal. In the example of FIG. 2, theAC input signal is demonstrated as including an in-phase AC input signalAC_(I) and a quadrature-phase AC input signal AC_(Q). As an example, thein-phase AC input signal AC_(I) and the quadrature-phase AC input signalAC_(Q) can collectively correspond to AC quadrature signals that areimplemented for RQL in quantum computing circuits. The DC output signalis demonstrated as a current I_(DC) that flows through an outputinductor L_(OUT).

Each of the stages 54, 56, 58, and 60 are configured substantiallysimilarly with respect to each other. The first stage 54 includes atransformer T₁, a first Josephson junction J₁ _(—) ₁, a second Josephsonjunction J₂ _(—) ₁, and a first inductor L_(X) _(—) ₁. The second stage56 includes a transformer T₂, a first Josephson junction J₁ _(—) ₂, asecond Josephson junction J₂ _(—) ₂, a first inductor L_(X) _(—) ₂, anda second inductor L_(Y) _(—) ₂. The third stage 58 includes atransformer T₃, a first Josephson junction J₁ _(—) ₃, a second Josephsonjunction J₂ _(—) ₃, a first inductor L_(X) _(—) ₃, and a second inductorL_(Y) _(—) ₃. The fourth stage 60 includes a transformer T₄, a firstJosephson junction J₁ _(—) ₄, a second Josephson junction J₂ _(—) ₄, afirst inductor L_(X) _(—) ₄, and a second inductor L_(Y) _(—) ₄.

The transformers T₁ and T₃ include a primary winding L₁ _(—) ₁ and L₁_(—) ₃, respectively, through which the in-phase AC input signal AC_(I)flows, and the transformers T₂ and T₄ include a primary winding L₁ _(—)₂ and L₁ _(—) ₄, respectively, through which the quadrature-phase ACinput signal AC_(Q) flows. The transformers T₁ and T₃ provide inductivecoupling of the in-phase AC input signal AC_(I) to the flux-shuttle loop52, and the transformers T₂ and T₄ provide inductive coupling of thequadrature-phase AC input signal AC_(Q) to the flux-shuttle loop 52.Therefore, the first transformer T₁ can generate a bias current I_(B1)via a secondary winding L₂ _(—) ₁ and the third transformer T₃ cangenerate a bias current I_(B3) via a secondary winding L₂ _(—) ₃ inresponse to the in-phase AC input signal AC_(I). Similarly, the secondtransformer T₂ can generate a bias current I_(B2) via a secondarywinding L₂ _(—) ₂ and the fourth transformer T₄ can generate a biascurrent I_(B4) via a secondary winding L₂ _(—) ₄ in response to thequadrature-phase AC input signal AC_(Q).

As an example, each of the first in-phase AC input signal AC_(I) and thequadrature-phase AC input signal AC_(Q) can include a positive portion(e.g., in a first half of a respective period) and a negative portion(e.g., in a second half of a respective period). As demonstrated in theexample of FIG. 2, the primary winding L₁ _(—) ₃ of the thirdtransformer T₃ has a polarity that is opposite the polarity of theprimary winding L₁ _(—) ₁ of the first transformer T₁. Similarly, theprimary winding L₁ _(—) ₄ of the fourth transformer T₄ has a polaritythat is opposite the polarity of the primary winding L₁ _(—) ₂ of thesecond transformer T₂. Therefore, the bias current I_(B1) is induced ina first direction via the second winding L₂ _(—) ₁ of the firsttransformer T₁ during the negative portion of the in-phase AC inputsignal AC_(I). However, because the primary windings L₁ _(—) ₁ andL3_(—)1 of the first and third transformers T₁ and T₃, respectively,have opposite polarities, the bias current I_(B3) is also induced in thefirst direction via the second winding L₂ _(—) ₃ of the thirdtransformer T₃ during the positive portion of the in-phase AC inputsignal AC_(I). Similarly, the bias current I_(B2) is induced in thefirst direction during the negative portion of the quadrature-phase ACinput signal AC_(Q), and the bias current I_(B4) is also induced in thefirst direction during the positive portion of the quadrature-phase ACinput signal AC_(Q). Therefore, as described in greater detail in theexample of FIG. 3, the bias currents I_(B1), I_(B2), I_(B3), and I_(B4)are sequentially provided in each of 90° intervals of the AC inputsignals AC_(I) and AC_(Q). In the example of FIG. 2, the “firstdirection” is demonstrated as being in a same current direction as aninitialization bias current I_(B) _(—) _(IN), as described herein, andwhich is demonstrated as from left-to-right from the respectivesecondary windings L₂ _(—) ₁, L₂ _(—) ₂, L₂ _(—) ₃, and L₂ _(—) ₄.

The Josephson AC/DC converter 50 includes an initialization transformerT_(IN) that forms part of the first stage 54, demonstrated in theexample of FIG. 2 as replacing a second inductor (e.g., L_(Y) _(—) ₁).The Josephson AC/DC converter 50 is demonstrated as receiving aninitialization signal INTL that can be provided to the Josephson AC/DCconverter 50 to initialize the operation of the Josephson AC/DCconverter 50. As an example, the initialization signal INTL can be a DCsignal that is substantially continuously provided to the JosephsonAC/DC converter 50. In the example of FIG. 2, the initialization signalINTL is provided through the primary winding L₁ _(—) _(IN) of thetransformer T_(IN), which induces the initialization bias current I_(B)_(—) _(IN) to be provided from the secondary winding L₂ _(—) _(IN). Inthe example of FIG. 2, the initialization bias current I_(B) _(—) _(IN)is demonstrated as flowing through the first inductor L_(X) _(—) ₂.

The addition of the magnitude of the initialization bias current I_(B)_(—) _(IN) and the bias current I_(B2) can be sufficient to exceed acritical current of the Josephson junction J₁ _(—) ₂. For example,during a negative portion of the quadrature-phase AC input signalAC_(Q), the bias current I_(B2) and the initialization bias currentI_(B) _(—) _(IN) can combine to flow through the Josephson junction J₂_(—) ₂. In response, because the magnitude of the bias currents I_(B2)and I_(B) _(—) _(IN) exceed the critical current of the Josephsonjunction J₂ _(—) ₂, the Josephson junction J₂ _(—) ₂ triggers togenerate a single-flux quantum (SFQ) pulse, which can be exhibited inthe flux-shuttle loop 52 as a voltage pulse. The SFQ pulse can thenpropagate from the second stage 56 to the third stage 58 through theinductors L_(Y) _(—) ₁ and L_(X) _(—) ₂ to trigger the first Josephsonjunction J₁ _(—) ₃. During the positive portion of the in-phase AC inputsignal AC_(I), the SFQ pulse can combine with the bias current I_(B3) totrigger the Josephson junction J₂ _(—) ₃. As a result, the Josephsonjunction J₂ _(—) ₃ generates the SFQ pulse. The Josephson junctions J₁and J₂ can thus continue to sequentially trigger based on the frequencyof the in-phase AC input signal AC_(I) and the quadrature-phase AC inputsignal AC_(Q). Accordingly, the SFQ pulse is sequentially generated ineach of the stages 54, 56, 68, and 60 at each 90° interval of the ACinput signals AC_(I) and AC_(Q).

In response to the SFQ pulse sequentially generated by the Josephsonjunction J₂ in each of the stages 54, 56, 58, and 60, a current pulse isgenerated in a storage inductor associated with the respective one ofthe stages 54, 56, 58, and 60. In the example of FIG. 2, the first stage54 includes a storage inductor L_(S) _(—) ₁, the second stage 56includes a storage inductor L_(S) _(—) ₂, the third stage 58 includes astorage inductor L_(S) _(—) ₃, and the fourth stage 60 includes astorage inductor L_(S) _(—) ₄. Thus, in response to the Josephsonjunction J₂ _(—) ₁ triggering, the SFQ pulse generates a resultingcurrent pulse I_(P1) in the storage inductor L_(S) _(—) ₁. In responseto the Josephson junction J₂ _(—) ₂ triggering, the SFQ pulse generatesa resulting current pulse I_(P2) in the storage inductor L_(S) _(—) ₂.In response to the Josephson junction J₂ _(—) ₃ triggering, the SFQpulse generates a resulting current pulse I_(P3) in the storage inductorL_(S) _(—) ₃. In response to the Josephson junction J₂ _(—) ₄triggering, the SFQ pulse generates a resulting current pulse I_(P4) inthe storage inductor L_(S) _(—) ₄. Each of the storage inductors L_(S)_(—) ₁, L_(S) _(—) ₂, L_(S) _(—) ₃, and L_(S) _(—) ₄ are coupled to theoutput inductor L_(OUT). As a result, the output inductor L_(OUT)integrates each of the current pulses I_(P1), I_(P2), I_(P3), and I_(P4)to provide the DC output signal I_(DC), such that the Josephson AC/DCconverter 50 acts as a current-limited DC signal source based on currentlimitation of the output inductor L_(OUT). As a result, the DC outputsignal I_(DC) can be provided as a DC signal converted from the in-phaseAC input signal AC_(I) and the quadrature-phase AC input signal AC_(Q)to a device (e.g., the device 12 in the example of FIG. 1).

FIG. 3 illustrates an example of a timing diagram 100. The timingdiagram 100 includes the in-phase AC input signal AC_(I) and thequadrature-phase AC input signal AC_(Q), as indicated at the legend 102,as a function of time. The in-phase AC input signal AC_(I) and thequadrature-phase AC input signal AC_(Q) are each demonstrated assinusoidal signals having magnitudes centered about zero. The in-phaseAC input signal AC_(I) and the quadrature-phase AC input signal AC_(Q)in the example of FIG. 3 can correspond to the in-phase AC input signalAC_(I) and the quadrature-phase AC input signal AC_(Q) in the example ofFIG. 2. Therefore, reference is to be made to the example of FIG. 2 inthe following description of the example of FIG. 3.

At a time t₀, a negative portion of the in-phase AC input signal AC_(I)begins, with a positive peak of the in-phase AC input signal AC_(I)occurring at a time t₁. Therefore, the in-phase AC input signal AC_(I)begins to induce the bias current I_(B1) via the secondary winding L₂_(—) ₁ in the first direction based on the inductive coupling with theprimary winding L₁ _(—) ₁. At a time just subsequent to the time t₁(e.g., based on the inductance of the transformer T₁), the magnitude ofthe bias current I_(B1), combined with the SFQ pulse provided by theJosephson junction J₁ _(—) ₁, exceeds the critical current of theJosephson junction J₂ _(—) ₁ having previously triggered, and thereforebecomes sufficient to trigger the Josephson junction J₂ _(—) ₁. As aresult, the Josephson junction J₂ _(—) ₁ generates the SFQ pulse, whichgenerates the current pulse I_(P1) in the storage inductor L_(S) _(—) ₁that is integrated by the output inductor L_(OUT) and propagates to thesecond stage to trigger the Josephson junction J₁ _(—) ₂.

Also, at the time t₁, a negative portion of the quadrature-phase ACinput signal AC_(Q) begins, with a positive peak of the quadrature-phaseAC input signal AC_(Q) occurring at a time t₂. Therefore, thequadrature-phase AC input signal AC_(Q) begins to induce the biascurrent I_(B2) via the secondary winding L₂ _(—) ₂ in the firstdirection based on the inductive coupling with the primary winding L₁_(—) ₂. At a time just subsequent to the time t₂ (e.g., based on theinductance of the transformer T₂), the magnitude of the bias currentI_(B2), combined with the SFQ pulse provided by the Josephson junctionJ₁ _(—) ₂ (and/or the initialization bias current I_(B) _(—) _(IN))exceeds the critical current of the Josephson junction J₂ _(—) ₂, andtherefore becomes sufficient to trigger the Josephson junction J₂ _(—)₂. As a result, the Josephson junction J₂ _(—) ₂ generates the SFQpulse, which generates the current pulse I_(P2) in the storage inductorL_(S) _(—) ₂ that is integrated by the output inductor L_(OUT) andpropagates to the third stage to trigger the Josephson junction J₁ _(—)₃.

Also, at the time t₂, a positive portion of the in-phase AC input signalAC_(I) begins, with a negative peak of the in-phase AC input signalAC_(I) occurring at a time t₃. Therefore, the in-phase AC input signalAC_(I) begins to induce the bias current I_(B3) via the secondarywinding L₂ _(—) ₃ in the first direction based on the inductive couplingwith the primary winding L₁ _(—) ₃ (e.g., opposite the polarity of theprimary winding L₁ _(—) ₁). At a time just subsequent to the time t₃(e.g., based on the inductance of the transformer T₃), the magnitude ofthe bias current I_(B3), combined with the SFQ pulse provided by theJosephson junction J₁ _(—) ₃, exceeds the critical current of theJosephson junction J₂ _(—) ₃, and therefore becomes sufficient totrigger the Josephson junction J₂ _(—) ₃. As a result, the Josephsonjunction J₂ _(—) ₃ generates the SFQ pulse, which generates the currentpulse I_(P3) in the storage inductor L_(S) _(—) ₃ that is integrated bythe output inductor L_(OUT) and propagates to the fourth stage totrigger the Josephson junction J₁ _(—) ₄.

Also, at the time t₃, a positive portion of the quadrature-phase ACinput signal AC_(Q) begins, with a negative peak of the quadrature-phaseAC input signal AC_(Q) occurring at a time t₄. Therefore, thequadrature-phase AC input signal AC_(Q) begins to induce the biascurrent I_(B4) via the secondary winding L₂ _(—) ₄ in the firstdirection based on the inductive coupling with the primary winding L₁_(—) ₄ (e.g., opposite the polarity of the primary winding L₁ _(—) ₂).At a time just subsequent to the time t₄ (e.g., based on the inductanceof the transformer T₄), the magnitude of the bias current I_(B4),combined with the SFQ pulse provided by the Josephson junction J₁ _(—)₄, exceeds the critical current of the Josephson junction J₂ _(—) ₄, andtherefore becomes sufficient to trigger the Josephson junction J₂ _(—)₄. As a result, the Josephson junction J₂ _(—) ₄ generates the SFQpulse, which generates the current pulse I_(P4) in the storage inductorL_(S) _(—) ₄ that is integrated by the output inductor L_(OUT) andpropagates to the first stage to trigger the Josephson junction J₁ _(—)₁.

Also, at the time t₄, a negative portion of the in-phase AC input signalAC_(I) begins. Therefore, the process of converting the in-phase ACinput signal AC_(I) and the quadrature-phase AC input signal AC_(Q)repeats, such that the time t₄ is equivalent to the time t₀, asdescribed previously. Accordingly, the Josephson junctions J₁ _(—) ₁, J₂_(—) ₁, J₁ _(—) ₂, J₂ _(—) ₂, J₁ _(—) ₃, J₂ _(—) ₃, J₁ _(—) ₄, and J₂_(—) ₄ can sequentially trigger to propagate the SFQ pulse around theflux-shuttle loop 52 to continuously provide the current pulses I_(P1),I_(P2), I_(P3), and I_(P4) in response to the triggering of the J₂ _(—)₁, J₂ _(—) ₂, J₂ _(—) ₃, and J₂ _(—) ₄, respectively, to the outputinductor L_(OUT) based on the frequency of the in-phase AC input signalAC_(I) and the quadrature-phase AC input signal AC_(Q). As a result, theoutput inductor L_(OUT) can integrate the current pulses I_(P1), I_(P2),I_(P3), and I_(P4) to provide the DC output signal I_(DC).

It is to be understood that the Josephson AC/DC converter 50 is notintended to be limited to the example of FIG. 2. As an example, the ACinput signal is not limited to being implemented as the in-phase ACinput signal AC_(I) and the quadrature-phase AC input signal AC_(Q), butcould instead be a single sinusoidal signal. As another example, theflux-shuttle loop 52 could include more or less than the four stages 54,56, 58, and 60, such as any multiple of two stages to accommodatepositive and negative portions of the AC input signal. Additionally,while the example of FIG. 2 demonstrates the in-phase andquadrature-phase AC input signals AC_(I) and AC_(Q) provided in oppositerespective polarities to sequentially provide the bias currents I_(B1),I_(B2), I_(B3), and I_(B4) at each of 90° intervals, other arrangementsof AC input signals can be implemented to provide the bias currentsI_(B1), I_(B2), I_(B3), and I_(B4) at each of 90° intervals. Forexample, the Josephson AC/DC converter 50 can implement four separate ACinput signals that are each 90° out of phase of each other, with thetransformers T₁ through T₄ all having the same polarity. Furthermore,other types of AC signals can be implemented for providing the DC outputsignal I_(DC), such as square wave signals and/or signals havingseparate frequencies with respect to each other. As yet another example,the stages 54, 56, 58, and 60 are not limited to the arrangementprovided in the example of FIG. 2, but could instead have a differentphysical arrangement with respect to the Josephson junctions J₁ and J₂,inductors Lx and L_(Y), transformers T₁ through T₄, and/or storageinductors L_(S). Accordingly, the Josephson AC/DC converter 50 can beconfigured in a variety of ways.

As demonstrated in the example of FIG. 2, the in-phase AC input signalAC_(I) and the quadrature-phase AC input signal AC_(Q) are demonstratedas passing through the primary windings L₁ _(—) ₁, L₁ _(—) ₂, L₁ _(—) ₃,and L₁ _(—) ₄ of the transformers T₁, T₂, T₃, and T₄, respectively.However, the in-phase AC input signal AC_(I) and the quadrature-phase ACinput signal AC_(Q) can, for example, be provided for a plurality ofJosephson AC/DC converters, such as to provide AC/DC conversion for aplurality of devices.

FIG. 4 illustrates an example of a superconducting circuit system 150.As an example, the superconducting circuit system 150 can be implementedin any of a variety of quantum computing applications, such as quantummemory or processing systems. The superconducting circuit system 150includes a plurality N of devices 152, where N is a positive integer.Each of the devices 152 receive a respective DC signal, demonstrated inthe example of FIG. 4 as respective DC currents I_(DC) _(—) ₁ throughI_(DC) _(—) _(N). As an example, the DC signals I_(DC) _(—) ₁ throughI_(DC) _(—) _(N) can be provided as power signals or as driver signalsto drive the devices 152. For example, the devices 152 can eachcorrespond to respective memory drivers, such as to provide read andwrite currents to an array of memory cells.

The superconducting circuit system 150 also includes a respectiveplurality of Josephson AC/DC converters 154 that are configured toconvert an AC input signal to the DC signals I_(DC) _(—) ₁ throughI_(DC) _(—) _(N). In the example of FIG. 4, the AC input signal isdemonstrated as an in-phase AC input signal AC_(I) and aquadrature-phase AC input signal AC_(Q), such as demonstrated in theexamples of FIGS. 2 and 3. As an example, each of the Josephson AC/DCconverters 154 can be configured substantially similar to the JosephsonAC/DC converter 50 in the example of FIG. 2. Therefore, the JosephsonAC/DC converters 154 can each include a flux-shuttle loop comprisingfour stages that are each configured substantially the same to propagatean SFQ pulse around the loop to generate current pulses that areintegrated into the respective DC output signals I_(DC) _(—) ₁ throughI_(DC) _(—) _(N) via respective output inductors. The Josephson AC/DCconverters 154 are also demonstrated as receiving an initializationsignal INTL that can be provided to the Josephson AC/DC converter 154 toinitialize the operation of the Josephson AC/DC converters 154 toconvert the in-phase AC input signal AC_(I) and the quadrature-phase ACinput signal AC_(Q) to the DC signals I_(DC) _(—) ₁ through I_(DC) _(—)_(N). In the example of FIG. 4, the same initialization signal INTL isprovided to each of the Josephson AC/DC converters 154, such that all ofthe Josephson AC/DC converters 154 operate together to generate the DCoutput signals IDC1 through I_(DC) _(—) _(N). However, it is to beunderstood that each of the Josephson AC/DC converters 154 can beprovided separate initialization signals INTL, such that the JosephsonAC/DC converters 154 can be independently controlled to providecombinations of the DC output signals I_(DC) _(—) ₁ through I_(DC) _(—)_(N). Additionally, while the Josephson AC/DC converters 154 arearranged in parallel in the example of FIG. 4, it is to be understoodthat the Josephson AC/DC converters 154 can instead be arranged inseries, such as to collectively generate a single DC output signalhaving an increased magnitude.

Similar to as described previously, the Josephson AC/DC converters 154can therefore operate to convert the in-phase AC input signal AC_(I) andthe quadrature-phase AC input signal AC_(Q) to the DC signals I_(DC)_(—) ₁ through I_(DC) _(—) _(N) in a power efficient manner based onhaving a lack of resistors. Therefore, the Josephson AC/DC converters154 only dissipate power via the current pulses to provide therespective DC signals I_(DC) _(—) ₁ through I_(DC) _(—) _(N) to thedevices 152, such that no additional power is dissipated to maintain theSFQ pulse propagating around the flux-shuttle loop in each of theJosephson AC/DC converters 154. In addition, the Josephson AC/DCconverters 154 can generate substantially no heat from static powerdissipation, as opposed to typical resistance-based DC power sources.Accordingly, the Josephson AC/DC converters 154 can operate efficientlyand effectively in the superconducting circuit system 150.

In view of the foregoing structural and functional features describedabove, a methodology in accordance with various aspects of the presentinvention will be better appreciated with reference to FIG. 5. While,for purposes of simplicity of explanation, the methodology of FIG. 5 isshown and described as executing serially, it is to be understood andappreciated that the present invention is not limited by the illustratedorder, as some aspects could, in accordance with the present invention,occur in different orders and/or concurrently with other aspects fromthat shown and described herein. Moreover, not all illustrated featuresmay be required to implement a methodology in accordance with an aspectof the present invention.

FIG. 5 illustrates an example of a method 200 for providing a DC outputsignal (e.g., the DC output signal I_(DC)) based on an AC input signal(e.g., the AC input signal AC). At 202, an initialization bias current(e.g., the initialization bias current I_(B) _(—) _(IN)) is provided toa flux-shuttle loop (e.g., the flux-shuttle loop 16) comprising aplurality of stages (e.g., the stages 54, 56, 58, and 60). At 204, theAC input signal that is inductively coupled with each of the pluralityof stages is provided. At 206, a Josephson junction (e.g., the Josephsonjunction J₂) associated with each of the plurality of stages issequentially triggered based on a frequency of the AC input signal tocirculate an SFQ pulse around the flux-shuttle loop to generate the DCoutput signal through an output inductor (e.g., the output inductorL_(OUT)).

What have been described above are examples of the invention. It is, ofcourse, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the invention,but one of ordinary skill in the art will recognize that many furthercombinations and permutations of the invention are possible.Accordingly, the invention is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims.

What is claimed is:
 1. An AC/DC converter system comprising: aflux-shuttle loop that is inductively coupled with an AC input signal;and a plurality of Josephson junctions spaced about the flux shuttleloop that are configured to sequentially trigger in response to the ACinput signal and to provide a single-flux quantum (SFQ) pulse that movessequentially around the flux-shuttle loop that results in a DC outputsignal being provided through an output inductor.
 2. The system of claim1, wherein the flux-shuttle loop further comprises a plurality oftransformers configured to inductively couple the flux-shuttle loop withthe AC input signal, wherein the AC input signal is provided through aprimary winding of each of the plurality of transformers to induce abias current in a secondary winding of each of the plurality oftransformers.
 3. The system of claim 2, wherein the primary winding ofeach of a first portion of the plurality of transformers have anopposite polarity relative to a primary winding of a second portion ofthe plurality of transformers, such that a second polarity portion ofthe AC input signal induces the bias current in a first direction in thesecondary winding of the first portion of the plurality of transformersand a first polarity portion of the AC input signal induces a biascurrent in the first direction in the secondary winding of the secondportion of the plurality of transformers.
 4. The system of claim 1,wherein the AC input signal comprises an in-phase AC input signal and aquadrature-phase AC input signal.
 5. The system of claim 4, wherein theflux-shuttle loop further comprises a plurality of transformersconfigured to inductively couple the flux-shuttle loop with each of thein-phase AC input signal and the quadrature-phase AC input signal,wherein the in-phase AC input signal is provided through a primarywinding of a first portion of the plurality of transformers to induce abias current in a secondary winding of the first portion of theplurality of transformers, and wherein the quadrature-phase AC inputsignal is provided through a primary winding of a second portion of theplurality of transformers to induce a bias current in a secondarywinding of the second portion of the plurality of transformers.
 6. Thesystem of claim 5, wherein the primary winding of each of the secondportion of the plurality of transformers has an opposite polarityrelative to a primary winding of the first portion of the plurality oftransformers, such that a second polarity portion of each of thein-phase AC input signal and the quadrature-phase AC input signalinduces a bias current in a first direction in the secondary winding ofthe second portion of the plurality of transformers, and a firstpolarity portion of each of the in-phase AC input signal and thequadrature-phase AC input signal induces a bias current in the firstdirection in the secondary winding of the first portion of the pluralityof transformers.
 7. The system of claim 1, wherein the flux-shuttle loopfurther comprises an initialization transformer having a secondarywinding configured to provide an initialization bias current in theflux-shuttle loop in response to an initialization signal that isprovided through a primary winding of the initialization transformer. 8.The system of claim 7, wherein the flux-shuttle loop comprises aplurality of stages, each of the plurality of stages comprises aplurality of Josephson junctions and a transformer configured toinductively couple the respective one of the plurality of stages withthe AC input signal, wherein a first of the plurality of stages includesthe initialization transformer, such that a current pulse generated viathe SFQ pulse at the first of the plurality of stages is provided to asecond of the plurality of stages via the secondary winding of theinitialization transformer.
 9. The system of claim 1, wherein theflux-shuttle loop comprises a plurality of stages, each of the pluralityof stages comprising: a transformer configured to generate a biascurrent based on inductive coupling of the AC input signal; a Josephsonjunction configured to trigger to generate a current pulse in responseto the bias current; and a storage inductor interconnecting therespective one of the plurality of stages with the output inductor andbeing configured to provide the current pulse to the output inductor.10. A superconducting circuit system comprising a plurality of the AC/DCconverter system of claim 1, the plurality of AC/DC converter systemsbeing configured to generate a respective plurality of DC outputsignals.
 11. A method for providing a DC output signal based on an ACinput signal, the method comprising: providing an initialization biascurrent to a flux-shuttle loop comprising a plurality of stages;providing the AC input signal that is inductively coupled with each ofthe plurality of stages; and sequentially triggering a Josephsonjunction associated with each of the plurality of stages in response tothe AC input signal to circulate a single-flux quantum (SFQ) pulsearound the flux-shuttle loop to generate the DC output signal through anoutput inductor.
 12. The method of claim 11, wherein providing the ACinput signal comprises providing the AC input signal to a primarywinding of each of a plurality of transformers that are each associatedwith one of the respective plurality of stages to induce a bias currentin a secondary winding of each of the plurality of transformers.
 13. Themethod of claim 12, wherein providing the AC input signal to the primarywinding comprises: providing the AC input signal to the primary windingof each of a first portion of the plurality of transformers to inducethe bias current in the secondary winding in a first direction inresponse to a first polarity portion of the AC input signal; andproviding the AC input signal to the primary winding of each of a secondportion of the plurality of transformers to induce the bias current inthe secondary winding in the first direction in response to a secondpolarity portion of the AC input signal.
 14. The method of claim 11,wherein providing the AC input signal comprises providing an in-phase ACinput signal and a quadrature-phase AC input signal.
 15. The method ofclaim 11, wherein providing the initialization signal comprisesproviding a DC initialization signal through a primary winding of theinitialization transformer to induce a bias current in the flux-shuttleloop.
 16. The method of claim 11, wherein providing the initializationsignal comprises providing the initialization signal to a flux-shuttleloop associated with each of a plurality of AC/DC converters, whereinproviding the AC input signal comprises providing the AC input signal toeach of the plurality of AC/DC converters, and wherein sequentiallytriggering the Josephson junction associated with each of the pluralityof stages comprises sequentially triggering a Josephson junctionassociated with each of the plurality of stages of the flux-shuttle loopassociated with each of the plurality of AC/DC converters to generate aDC output signal through an output inductor associated with each of theplurality of AC/DC converters.
 17. An AC/DC converter system comprising:a flux-shuttle loop comprising a plurality of stages and beingconfigured to receive an AC input signal, each of the plurality ofstages comprising: a transformer configured to generate a bias currentbased on inductive coupling of the AC input signal to the respective oneof the plurality of stages; a Josephson junction configured to triggerto provide a single-flux quantum (SFQ) pulse in response to the biascurrent; and a storage inductor that is interconnected with the outputinductor and configured to provide a current pulse output in response tothe SFQ pulse; and an output inductor coupled to each of the storageinductors and being configured to provide the DC output signal based onthe received current pulse outputs that are sequentially provided fromeach of the storage inductors.
 18. The system of claim 17, wherein thetransformer associated with each of the plurality of phases isconfigured to generate the bias current in a sequence through each ofthe plurality of stages based on the frequency of the AC input signal,such that the Josephson junction associated with each of the pluralityof phases is configured to trigger in the sequence to provide the SFQpulse around the flux-shuttle loop.
 19. The system of claim 17, whereinthe AC input signal comprises an in-phase AC input signal and aquadrature-phase AC input signal, wherein the in-phase AC input signalis provided through a primary winding of the transformer in each of afirst portion of the plurality of stages to induce the bias current in asecondary winding of the transformer in each of the first portion of theplurality of stages, and wherein the quadrature-phase AC input signal isprovided through a primary winding of the transformer in each of asecond portion of the plurality of stages to induce the bias current ina secondary winding of the transformer in each of the second portion ofthe plurality of stages.
 20. The system of claim 19, wherein the primarywinding of the transformer in each of a first portion of the pluralityof stages has an opposite polarity relative to the primary winding ofthe transformer in each of second portion of the plurality of stages,such that a second polarity portion of each of the in-phase AC inputsignal and the quadrature-phase AC input signal induces a bias currentin a first direction in the secondary winding of the transformer in eachof second portion of the plurality of stages, and a first polarityportion of each of the in-phase AC input signal and the quadrature-phaseAC input signal induces a bias current in the first direction in thesecondary winding of the transformer in each of first portion of theplurality of stages.